I agreed with your opinion that bitcoin surely controlable although that this coin is volatile and kinda risky. Bank investment in my knowledge does have some kind of contract that you can't pull your investment anytime.
The only risk is that the rate can not be guessed at 100%. Therefore, you can lose all the money for 1 day. If you know how to understand the exchange rate, you can get a big profit. Therefore, if a person is illiterate in this case, then it is better to put money into the bank.